This invention relates generally to the art of paper sheet handling, and more particularly concerns a multiple position bidirectional idler roller for use in a sheet inverter system.
The invention is especially suited for use in the paper handling and inverter system of an electrophotographic printing machine and will be described with reference thereto; however, as will become apparent, the invention could be used in many types of paper sheet handling systems in a variety of different machines.
Although a sheet inverter is referred to in the copier/printer art as an xe2x80x9cinverterxe2x80x9d, its function is not necessarily to immediately turn the sheet over (i.e., exchange one face for the other). Its function is to effectively reverse the sheet orientation in its direction of motion. That is, to reverse the lead and trail edge orientation of the sheet. Typically, in inverters as disclosed here, the sheet is driven or fed by feed rollers or other suitable sheet driving mechanisms into a sheet reversing chute. By then reversing the motion of the sheet within the chute and feeding it back out from the chute, the desired reversal of the leading and trailing edges of the sheet in the sheet path is accomplished. Depending on the location and orientation of the inverter in a particular sheet path, this may, or may not, also accomplish the inversion (turning over) of the sheet. In some applications, for example, where the xe2x80x9cinverterxe2x80x9d is located at the comer of a 90xc2x0 to 180xc2x0 inherent bend in the copy sheet path, the inverter may be used to actually prevent inverting of a sheet at that point, i.e., to maintain the same side of the sheet face-up before and after this bend in the sheet path. On the other hand, if the entering and departing path of the sheet, to and from the inverter, is in substantially the same plane, the sheet will be inverted by the inverter. Thus, inverters have numerous applications in the handling of either original documents or copy sheets to either maintain, or change, the sheet orientation.
In the field of reprographic machines, it is often necessary to feed a copy sheet leaving the processor of the machine along one of two alternate paths, particularly when the machine can selectively produce simplex (one-sided) and duplex (two-sided) sheets. Simplex sheets may be fed directly to an output tray, whereas duplex sheets may pass to a sheet feeder, which automatically reverses the direction of movement of a simplex sheet and feeds it back into the processor, but inverted, so that the appropriate data can be applied to the second side of the sheet.
Many inverters, particularly those utilizing only spring action or gravity, have reliability problems in the positive output or return of the sheet at a consistent time after the sheet is released from the inverter. Furthermore, inverter reliability problems are aggravated by variations in the condition or size of the sheet. For example, a pre-set curl in the sheet can interfere with feed-out and even cause the sheet to assume an undesirable configuration when it is released.
Paper curl is defined as any deviation from its flat state. In the xerographic process, fusing drives moisture out. When regaining moisture, paper experiences curl due to differential hygroexpansivity and thermoexpansivity between the paper and toner, and dimensional instability of paper due to its moisture history. The paper expands due to moisture reabsorption, but the toner does not expand, thus developing curl. Paper curl is one of the primary causes for paper handling problems in copying machines. In an inverter, problems such as stubbing result from copy sheet curl These problems are more severe for color copies than black and white due to differences in their toner mass area, substrates, and fuser characteristics.
The use of a curved chute within an inverter, i.e., curved sheet guides or baffles to define the reversing chamber for the sheet, will not necessarily insure the proper orientation of the trail edge of the sheet relative to the exit nip, or the leading edge of the sheet relative to the inverter nip. Also, different weights or thickness of paper will have different beam strengths, i.e. different self-straightening forces.
It is desirable to develop a new and improved sheet inverter apparatus which overcomes the above noted problems and others encountered in the prior art. The present invention meets these needs and others and provides a bi-directional inverter nip which is simple and not likely to damage the documents handled therein.
The following disclosures may relate to various aspects of the present invention:
U.S. Pat. No. 5,720,478 to Carter et al., teaches a gateless sheet inverter in which a curved portion of the sheet path branch intersects a second portion of the sheet path to form a curved inverter throat. As the sheet is driven from the curved branch portion of the path into the throat portion, the beam strength of the sheet causes the trail edge of the sheet to flip toward a second nip leading to the second sheet path. A pair of reversing rollers captures the lead edge of the sheet to be inverted and then reverses to drive the sheets out of the second nip formed by the tri-roller arrangement.
U.S. Pat. No. 5,382,013 to Walsh, discloses a paper inverter system having a clutch-driven inverter nip for maintaining a positive bidirectional contact with the sheet. A pair of opposing rollers defines a nip, with a shaft connected to one of the pair of opposing rollers. The clutch couples one end of the shaft to a drive system while the other end of the shaft is connected to a spring, which resists rotation of the shaft. The drive system rotates the shaft in a first rotational direction against the spring force. The clutch then decouples the shaft from the drive system for rotation in the opposing direction with the spring force.
U.S. Pat. No. 5,374,049 to Bares et al., discloses an inverter comprised of a reversible roller onto which a sheet is scrolled and subsequently unscrolled, thereby reversing the lead and trail edges of the sheet.
U.S. Pat. No. 5,317,377 to Rubscha et al., discloses a tri-roller inverter in which a passive deflector gate is deflected by a sheet driven by the input nip. The gate is deflected to an open position, which allows the sheet to enter the inversion chute. After the sheet is past the gate, the gate returns to a closed position, thus allowing the sheet to be driven past it in reverse by a reversing roller.
In accordance with one aspect of the present invention, there is provided an inverter for reversing the direction of a sheet moving along a paper path. The inverter includes a drive roller and an idler roller in circumferential contact in at least two positions. A nip is defined in each position.
In accordance with another aspect of the invention, there is provided a method of operating an inverter for reversing the orientation of a moving paper sheet. The method comprises receiving a lead edge of a moving sheet into a continuously driven first nip, which includes a continuously driven main drive roller and a first idler roller. A bi-directionally driven nip, which includes a forward/reverse driven roller and a multiple position idler roller, is then driven in a first direction to receive the lead edge of the sheet into the bidirectional nip. The forward/reverse driven roller then reverses to a second direction, thereby moving the trailing edge of the moving paper sheet into a second continuously driven nip having a continuously driven main drive roller and a second idler roller to expel the sheet from the inverter.
Pursuant to yet another aspect of the present invention, there is provided an electrophotographic printing machine having a device for inverting a sheet along a paper path. The inverting device includes a drive roller and an idler roller in circumferential contact in at least two positions. A nip is defined in each position.